6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
[ Upstream commit b23decf8ac9102fc52c4de5196f4dc0a5f3eb80b ]
Idle tasks are initialized via __sched_fork() twice:
fork_idle()
copy_process()
sched_fork()
__sched_fork()
init_idle()
__sched_fork()
Instead of cleaning this up, sched_ext hacked around it. Even when analyis
and solution were provided in a discussion, nobody cared to clean this up.
init_idle() is also invoked from sched_init() to initialize the boot CPU's
idle task, which requires the __sched_fork() invocation. But this can be
trivially solved by invoking __sched_fork() before init_idle() in
sched_init() and removing the __sched_fork() invocation from init_idle().
Do so and clean up the comments explaining this historical leftover.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20241028103142.359584747@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/sched/core.c | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 228f7c07da72..86606fb9e6bc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4488,7 +4488,8 @@ int wake_up_state(struct task_struct *p, unsigned int state)
* Perform scheduler related setup for a newly forked process p.
* p is forked by current.
*
- * __sched_fork() is basic setup used by init_idle() too:
+ * __sched_fork() is basic setup which is also used by sched_init() to
+ * initialize the boot CPU's idle task.
*/
static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
{
@@ -9257,8 +9258,6 @@ void __init init_idle(struct task_struct *idle, int cpu)
struct rq *rq = cpu_rq(cpu);
unsigned long flags;
- __sched_fork(0, idle);
-
raw_spin_lock_irqsave(&idle->pi_lock, flags);
raw_spin_rq_lock(rq);
@@ -9273,10 +9272,8 @@ void __init init_idle(struct task_struct *idle, int cpu)
#ifdef CONFIG_SMP
/*
- * It's possible that init_idle() gets called multiple times on a task,
- * in that case do_set_cpus_allowed() will not do the right thing.
- *
- * And since this is boot we can forgo the serialization.
+ * No validation and serialization required at boot time and for
+ * setting up the idle tasks of not yet online CPUs.
*/
set_cpus_allowed_common(idle, &ac);
#endif
@@ -10105,6 +10102,7 @@ void __init sched_init(void)
* but because we are the idle thread, we just pick up running again
* when this runqueue becomes "idle".
*/
+ __sched_fork(0, current);
init_idle(current, smp_processor_id());
calc_load_update = jiffies + LOAD_FREQ;
--
2.39.5
